Diffstat (limited to 'arch/Kconfig')
1 files changed, 25 insertions, 8 deletions
diff --git a/arch/Kconfig b/arch/Kconfig
index 4f55c73..684eb5a 100644
@@ -47,18 +47,29 @@ config KPROBES
If in doubt, say "N".
- bool "Optimize trace point call sites"
+ bool "Optimize very unlikely/likely branches"
depends on HAVE_ARCH_JUMP_LABEL
+ This option enables a transparent branch optimization that
+ makes certain almost-always-true or almost-always-false branch
+ conditions even cheaper to execute within the kernel.
+ Certain performance-sensitive kernel code, such as trace points,
+ scheduler functionality, networking code and KVM have such
+ branches and include support for this optimization technique.
If it is detected that the compiler has support for "asm goto",
- the kernel will compile trace point locations with just a
- nop instruction. When trace points are enabled, the nop will
- be converted to a jump to the trace function. This technique
- lowers overhead and stress on the branch prediction of the
+ the kernel will compile such branches with just a nop
+ instruction. When the condition flag is toggled to true, the
+ nop will be converted to a jump instruction to execute the
+ conditional block of instructions.
- On i386, options added to the compiler flags may increase
- the size of the kernel slightly.
+ This technique lowers overhead and stress on the branch prediction
+ of the processor and generally makes the kernel faster. The update
+ of the condition is slower, but those are always very rare.
+ ( On 32-bit x86, the necessary options added to the compiler
+ flags may increase the size of the kernel slightly. )
@@ -109,6 +120,9 @@ config HAVE_KRETPROBES
# An arch should select this if it provides all these things:
@@ -199,4 +213,7 @@ config HAVE_CMPXCHG_LOCAL